JP2019528417A - Method of forming a thermal switch - Google Patents

Abstract

(A) preparing a first conductor and a second conductor, and a first connecting member and a second connecting member, wherein each of the connecting members is at least 5 times the conductor at 100K. Having a low thermal conductivity; (b) fusing the first conductor with the first connecting member and the second conductor with the second connecting member; (c) the first conductor and Aligning the conductors such that the second conductors extend along a common major axis; and (d) bringing the proximal ends of the aligned conductors into contact with each other when the conductors are at a first temperature. And (e) joining the first connecting member to the second connecting member so as to form a chamber around at least the proximal end of the conductor to form a gas gap thermal switch A method is provided to form a chamber Each of the connecting members has a length of the conductor along the main axis such that a gap is formed between the proximal ends of the conductor when the conductor is cooled to a second temperature lower than the first temperature. Has a smaller coefficient of thermal expansion than the conductor so that it decreases with respect to the length of the chamber along the main axis, and the switch selectively introduces thermally conductive gas into the chamber to cause the switch to operate in use. Configured to supply. [Selection] Figure 5

Description

  The present invention relates to the field of cryogenic temperatures, and in particular, to a method for forming a gas gap thermal switch.

  Gas-gap thermal switches (or “thermal switches”) are known in the cryogenic field and are particularly useful in “cryogenic-free” systems, where cooling is not a liquefied gas, but a closed cycle mechanical cooling. Provided by the vessel. These switches can be controlled to transfer or block a thermal load from one end of the switch to the other. In general, these include at least two conductors separated from each other in a chamber into which a gas can be introduced. When the switch is closed, the gas inside the chamber helps heat transfer between the conductors by heat conduction. The switch is opened by evacuating the gas from the chamber and this heat transfer path is no longer available.

  In general, conductors take the form of interleaving or “comb” members, for example in the form of fins arranged to provide a large heat transfer surface between the conductors. A gap needs to exist between each conductor of the switch in order to be able to break the thermal connection when the switch is open. Nevertheless, this gap size must be kept to a minimum to achieve reliable heat transfer when the switch is closed. Switch performance is parameterized by the ratio (A / L) of effective heat exchange surface area divided by the separation distance (or gap) between each conductor. It is relatively difficult to produce high performance switches using a comb design, especially when the switches are miniaturized.

  Simpler designs for gas gap thermal switches have already been proposed, and the conductors are arranged on the same straight line rather than in a comb arrangement. In general, however, these switches are avoided, especially in low temperature applications, due to poor heat transfer characteristics in the closed state (limited by the gap size).

  It would be desirable to provide a simple gas gap thermal switch that can be reliably and easily configured and provides excellent performance at low temperatures.

In a first aspect of the invention, the following steps:
(A) preparing a first conductor and a second conductor, and a first connecting member and a second connecting member, wherein each of the connecting members is at least 5 times the conductor at 100K. A step having a low thermal conductivity; and
(B) fusing the first conductor with the first connecting member and the second conductor with the second connecting member;
(C) aligning the conductors such that the first conductor and the second conductor extend along a common major axis;
(D) bringing the proximal ends of the aligned conductors into contact with each other when the conductors are at a first temperature;
(E) joining the first connecting member to the second connecting member so as to form a chamber around at least the proximal end of the conductor;
A method is provided for forming a gas gap thermal switch comprising:
Each of the connecting members forming the chamber includes a conductor along the main axis such that a gap is formed between the proximal ends of the conductor when the conductor is cooled to a second temperature lower than the first temperature. Having a smaller coefficient of thermal expansion than the conductor so that the length of the is reduced relative to the length of the chamber along the main axis
The switch is configured to selectively supply a thermally conductive gas into the chamber to cause activation of the switch in use.

  Unlike the comb-shaped prior art designs, the conductors are aligned (e.g., collocated) to extend along a common major axis. Thus, the thermally conductive gas only transfers heat between the opposing proximal ends of the conductors, rather than along the entire length of each conductor. However, this reduction in effective heat transfer surface is compensated by a smaller separation distance between the opposing conductors than was possible with conventional reliable thermal switches. Thus, effective heat transfer across the switch can be maintained, while at the same time ensuring a secure and detachable thermal connection.

  In this specification, a heat-shrinkable gas gap type thermal switch is proposed, and the distance between conductors arranged on the same collinear line can be controlled according to the temperature of the conductor. Advantageously, the switch can be assembled at room temperature (in this case the first temperature). Once assembled, the switch can then be cooled so that the conductor can shrink relative to the sleeve due to the difference in coefficient of thermal expansion between the sleeve and the conductor. Thus, a small gap is created between the opposite ends of each conductor. Heat transfer occurs in this gap mainly by heat conduction using a thermally conductive gas.

  In general, steps (a) to (e) are performed in sequence, but step (c) can be performed before step (b). In either case, stage (b) is performed before steps (d) and (e). In general, step (e) is performed when the proximal ends of the aligned conductors are in contact with each other, i.e. after step (d).

  Step (e) initially relates to the process of joining the separate connecting members together. According to one approach, step (e) includes fusing the first connecting member to the second connecting member. Thus, these components can be joined together directly. Preferably, the first or second connecting member can include a sleeve portion configured to surround at least the proximal ends of the first and second conductors. In this case, the first and second connecting members together form a chamber wall that defines the chamber.

  In general, fusing each connecting member together will input heat to the switch. It is advantageous to ensure that this heat is not conducted across the length of the conductor, and therefore a highly localized heating process such as electron beam welding is performed on these joints. Therefore, preferably, the fusion of the first connecting member to the second connecting member is performed using electron beam welding. This can allow the conductor to remain within approximately the first temperature, eg, an average value of about 20K, during step (e).

  In an alternative approach, step (e) includes fusing each of the first and second connecting members to a sleeve disposed between the connecting members, wherein the thermal conductivity of the sleeve is greater than the conductor at 100K. When at least 5 times smaller and when the conductor is cooled to a second temperature, the thermal expansion coefficient of the sleeve is smaller than that of the conductor so that the length of the conductor along the main axis is reduced so that the gap described above is formed. Thus, the intermediate sleeve can be provided to form part of the chamber. Thus, the first and second connecting members can be joined together indirectly by step (e). This method generally requires the creation of additional joints to fuse each of the connecting members to the sleeve (preferably using electron beam welding as well), but in some cases thermal switches And depending on the shape and size of any accompanying device, it can be more easily assembled. Preferably, the first and second connecting members form first and second flanges, respectively. These flanges can be arranged to close the open end of the sleeve during use. The first and second connecting members and the sleeve can together form a chamber wall, thus defining the chamber of this embodiment, and the flange functions as the respective opposite end of the chamber. The sleeve itself can be a single piece or formed from several parts.

  It would be advantageous to ensure that no significant heat exchange path was established along the sleeve, as it would effectively bypass the opening of the switch by bypassing the conductor and gap. Accordingly, the sleeve (as a separate member or part of the connecting member) preferably has a thermal conductivity at 100K that is at least 10 times less than the conductor. Since the thermal conductivity of different materials tends to be different at low temperatures, the sleeve can have a thermal conductivity that is at least 1000 times less than the conductor when at a temperature of 10K. For similar reasons, the first and second connecting members preferably have a thermal conductivity that is at least 10 times less than the conductor when at a temperature of 100K. Preferably, the first and second connecting members have a thermal conductivity that is at least 1000 times less than the conductor when at a temperature of 10K.

  Preferably, the conductor is copper or copper-based (including oxygen free copper) due to high thermal conductivity and thermal expansion properties. Preferably, the connecting member is stainless steel because it exhibits desirable thermal conductivity and thermal expansion characteristics compared to copper. Stainless steel is also desirable because it exhibits excellent weldability. Also preferably, the sleeve is made of stainless steel for similar reasons.

  Preferably, the method reduces the length of the conductor along the major axis so as to cool each of the conductors to a respective temperature below the second temperature to form a gap between the proximal ends of the conductors. The step (f) of reducing is further included. This step is typically performed by the end user of the gas gap thermal switch, installed at the operating site and connected to, for example, a mechanical refrigerator for cooling. Cooling can be applied directly to one of the conductors by an external member during this phase, and the switch is kept closed to allow heat transfer to occur from the other conductor. Alternatively, both conductors can be cooled directly during this stage. Most typically, the temperature difference is maintained across the switch so that each of the two conductors is at a different temperature below the second temperature.

  It is desirable to ensure that the path length that the gas travels between opposing conductors is kept to a minimum. It is therefore advantageous to achieve a uniform gap size between the opposing surfaces of the conductor.

  Thus, step (a) can further include machining the first and second conductors to form a flat engagement surface on each conductor, and step (d) includes the engagement described above. The steps may include bringing the surfaces into contact with each other. In addition, the curved engagement surface can theoretically be used to obtain a uniform gap size from all points on the engagement surface of the abutting conductor. It is preferable because it can be processed. Most preferably, the engagement surface described above extends in a plane having a normal extending along the main axis of the respective conductor.

  The gap can be thought of as the closest point between all opposing surfaces of the first and second conductors. For conductors having opposing (engaging) surfaces perpendicular to the main axis, this gap will be measured along the main axis, but in other cases, the gap is between two conductors. It can be measured along different directions depending on the minimum separation distance.

  The gap is formed by thermal contraction of the conductor along these major axes. Accordingly, the first and second conductors are preferably elongated to ensure that applicable contraction occurs such that the two conductors do not contact each other directly at the second temperature.

  Most typically, the gap is 0. 0 of the total conductor dimension along the principal axis between each junction of the first conductor having the first connecting member and the second conductor having the second connecting member. Less than 05%. Since the conductors and connecting members can have multiple junctions or extensive junction areas, the associated junction is closest to the proximal end of each conductor. It is this point that results in a zero cross-strain position between the joining components, whereas a relative heat shrinkage difference occurs. Conductors with dimensions on the order of a few centimeters along the main axis can produce gap sizes on the order of a few micrometers, resulting in excellent heat transfer due to the thermally conductive gas between the conductors. .

  Step (b) is preferably performed by a brazing process. Such a process creates a convenient strong joint during thermal cycling. This process can also produce joints that are resistant to gas leakage and can contribute to chamber sealing. In particular, vacuum brazing is preferred because it has high integrity and strength and produces a very clean and flux free brazed joint. The heat input during step (b) (and the associated thermal expansion of the conductor) does not cause problems because the conductor is not in contact-step (d).

  Preferably, the switch is configured to evacuate the chamber when used to substantially thermally insulate the opposite distal end of the conductor. This step effectively “opens” the switch so that negligible heat transfer occurs between the two conductors of the switch. Other evacuation means including gas pumps or adsorption pumps and getters can be provided to assist in this process. Optionally, getters and / or adsorption pumps can be integrated into the switch to provide a sealing unit.

  Most typically, the first temperature is 280-310K. Thus, advantageously, the switch can be assembled at about room temperature. The gap between the two aligned conductors occurs at a low temperature, which is the second temperature. This second temperature can be considered the operating temperature of the thermal switch that can open and close the switch. The switch may still be useful at a temperature higher than the second temperature, for example, to form a heat transfer path along the conductors in contact with each other to help cool the system to a lower temperature. it can. The second temperature can include any temperature below 100K, but is most typically 5-20K. Since the purpose of the switch is to selectively thermally isolate one end of the switch from the other end, each end of the switch when in the “open” state is different below a second temperature, respectively. It can be temperature.

In the second aspect of the present invention,
First and second conductors aligned along a common major axis, each having a length of at least 5 cm along the major axis;
A first connecting member and a second connecting member forming a chamber around at least the proximal end of the conductor, wherein the connecting member has a thermal conductivity at 100K that is at least five times less than the conductor;
A gas gap thermal switch including is provided,
Each of the connecting members has a smaller coefficient of thermal expansion than the conductor;
The proximal end of the first conductor is separated from the proximal end of the second conductor by a gap of less than 50 μm;
In use, the switch is configured to selectively supply a thermally conductive gas into the chamber to activate the switch.

  Preferably, the gap is less than 30 micrometers, which allows for better heat transfer by the thermally conductive gas between the opposing conductors.

Preferably, the gas gap thermal switch of the second aspect further includes a sleeve provided between the connecting members described above and disposed to extend at least above the proximal end of the conductor,
Each of the first and second connecting members is fused to the sleeve;
The sleeve has a thermal conductivity at least 5 times smaller than the conductor at 100K,
The sleeve has a smaller coefficient of thermal expansion than the conductor;
The sleeve and connecting member form a chamber.

In the third aspect of the present invention,
A gas gap thermal switch according to the second aspect;
A mechanical refrigerator connected to the first conductor; a target device connected to the second conductor;
A cryogenic system is provided.

  In some embodiments, the third aspect can provide faster cooling times for the target device than can be achieved using some prior art gas gap thermal switches. The target device can theoretically be any element that is cooled, including an additional stage of a mechanical refrigerator.

  The second and third aspects of the invention can share similar features of the first aspect and the same advantages are applied by similarity.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

It is sectional drawing of a 1st conductor and a 1st connection member. It is sectional drawing of the 1st and 2nd conductor arrange | positioned inside a sleeve. It is sectional drawing of embodiment of a gas gap type thermal switch. 1 is a schematic diagram of a cryogenic system according to one embodiment. FIG. 2 is a flowchart illustrating a method according to one embodiment. It is sectional drawing of one Embodiment of a gas gap type thermal switch.

  An embodiment of a method for forming a heat shrink gas gap thermal switch 10 and an embodiment of the switch 10 will be described with reference to the flowchart of FIG. 5 and the accompanying drawings of FIGS. Become.

  The first and second conductors 2, 3 are prepared in step 300 of FIG. A cross-sectional view of a first connecting member in the form of a first conductor 2 and a first flange 4 is presented in FIG. The first conductor 2 is elongated and substantially cylindrical. The first flange 4 includes a central bore having a diameter of about 1 cm, which engages the first end portion 11 of the first conductor 2. The first end portion 11 has a diameter of 1 cm along its length and the remaining portion of the conductor 2 has a larger constant diameter of 2 cm along its length, so that the first One flange 4 is fitted over and around the first end portion 11 as a mere collar. The first end portion 11 includes a central bore 18 to allow physical connection of the conductor 2 to a connection member such as a mechanical refrigerator or target device, whereby heat is transferred. This physical connection can be achieved to some extent by fastening a plurality of bolts that extend through the first flange 4 and into the pitch circle of the bolt holes 9 provided in the first end portion 11. .

  A similar second conductor 3 (not shown in FIG. 1) is provided, which engages a second connecting member in the form of a second flange 5 in a similar manner. Each conductor 2, 3 has a length of about 5 cm along its main axis. In alternative embodiments, the conductors 2, 3 can have different lengths along their respective major axes.

  The first and second conductors 2 and 3 are fused to the first and second flanges 4 and 5 in step 301, respectively. Preferably, the first flange 4 is vacuum brazed over the first end portion 11 of the conductor 2 to achieve a strong and reliable permanent connection against thermal cycling. Apart from this, the process is then repeated for the second conductor 3 using the second flange 5.

  In order to allow heat transfer along the switch, each of the first and second conductors 2, 3 is formed from a highly thermally conductive material. If it is intended to use the switch at low temperatures, including temperatures below 100K, this means that the conductors 2, 3 need to be highly thermally conductive at such low temperatures. In general, each of the first and second conductors 2, 3 is formed from the same material, ensuring similar heat conduction and expansion characteristics. Most commonly, this material is copper, preferably oxygen-free copper, but in principle silver can also be used. Ideally, the conductor will have a thermal conductivity of 5000 W / mK or higher at a temperature of 20K.

  The first and second conductors 2, 3 are aligned in step 302 (in this case “collocated”) so as to extend along a common principal axis (or “longitudinal axis”), As a result, the first end portions 11, 12 are arranged at the opposite distal ends of the conductors 2, 3 and the flanges are provided at these ends. The brazing process can input heat to the conductors 2, 3 which expand the conductors 2, 3. The operator must wait for this heat to dissipate from the conductors 2, 3 before starting step 303.

  An annular sleeve 6 is provided having an inner diameter that is partially larger than the diameter of the conductors 2, 3. The length of the sleeve along its main axis is shorter than the switch length formed by the sum of the dimensions of the conductors 2, 3 along these main axes. In this case, the switch length is about 10 cm and the sleeve length is about 9 cm along the main axis.

  In step 303 of FIG. 5, the conductors 2, 3 are then at room temperature (or 290-300K) until the ends 13, 14 of the conductors 2, 3 in close proximity to each other are in mutual contact at the first temperature. Are brought together or “pressed” inside the sleeve 6 at a first temperature which is Accordingly, the respective main axes of the conductors 2, 3 and the sleeve 6 are aligned along the common main axis at this stage. The sleeve 6 is preferably a unitary structure (i.e. formed as a single piece), but can alternatively be composed of several parts. In an alternative assembly process, the conductors 2, 3 are first placed on the same straight line, and then the sleeve 6 slides on one of the connecting members or surrounds the conductors 2, 3. 3 is assembled around.

  The first and second conductors 2 and 3 are arranged such that there is no gap between the contact surfaces of the conductors 2 and 3 at the first temperature. In this embodiment, this ensures that the conductors 2, 3 have a flat surface (or “engagement surface”) at the proximal ends 13, 14 perpendicular to the main axis of the conductors 2, 3 that abut together. Is achieved. This flatness uniformity and precision can be achieved using machining prior to assembly in step 303 (before or after step 301). Other shaped surfaces are possible if the proximal ends 13, 14 of the conductors 2, 3 mesh with each other so as not to leave a macroscopic gap when pressed together. Preferably, each engagement surface has the same surface area and is arranged such that the radial surfaces of the conductors 2, 3 are coplanar at the proximal ends 13, 14.

  The sleeve 6 and the flanges 4, 5 form a housing that defines a chamber 16 in the region between the first flange 4 and the second flange 5. Specifically, since the inner diameter of the sleeve 6 is larger than the outer diameter of the conductors 2 and 3 by, for example, 1 mm, the annular chamber 16 is formed along the length of the conductors 2 and 3.

  In step 304, the sleeve 6 is fused over the first and second flanges 4, 5 to form the sealed chamber 16 and thereby form the switch 10. The sleeve 6 is joined to the flanges 4, 5 at each end of the sleeve 6 using a localized heating process such as electron beam welding. Advantageously, there is no significant heat input to the conductors 2, 3 that would cause them to expand during this process.

  The flanges 4, 5 and the sleeve 6 are formed from a material that insulates at a lower temperature than the conductors 2, 3, so that they are in the heat transfer path between the opposed distal ends 11, 12 of the switch 10. Does not form part. Specifically, the thermal conductivity of the conductors 2, 3 should be at least 5 times greater than the flanges 4, 5 and sleeve 6 at a temperature of 100K. Since the thermal conductivity tends to differ between different materials at low temperatures, this difference may be even greater by a factor of 1000 at a temperature of 10K, for example. A suitable candidate material for the flanges 4, 5 and sleeve 6 is stainless steel with the additional advantage of providing good weldability. Most preferably, each of the flanges 4, 5 and the sleeve 6 is formed from the same material to exhibit similar thermal conductivity and expansion / contraction characteristics.

  Importantly, the sleeve 6 is fused to the stainless steel flanges 4, 5 and not directly to the copper conductors 2, 3. The flanges 4, 5 (which have a lower thermal conductivity than the conductors 2, 3) serve as thermal barriers that reduce the amount of heat conducted along the length of the conductors 2, 3 during the fusion process. Thus, any heating is localized, and expansion of the conductors 2, 3 as a result of thermal expansion during the fusion process of step 304 is substantially avoided. Thus, contact between the conductors 2, 3 is achieved at a first temperature (not the temperature raised by heat input from the fusion process). The benefits of this will become clear later.

  In step 305, the switch 10 is installed at the operating location and the first and second conductors 2, 3 are cooled. For example, the cryogenic refrigerator may be connected to either or both of the conductors 2, 3 at the respective distal ends 11, 12 of the thermal switch 10 using a bore 18 (optionally additional connecting bolts). it can. The chamber 16 can be filled at this stage with a thermally conductive gas, typically helium at 1 bar absolute pressure. For low temperature applications of about 10 mK, helium-3 is preferred because it has a much lower superfluid transition temperature than helium-4 and is therefore less likely to cause undesirable thermal shorts. However, any gas can be used.

  The thermal switch 10 is configured to selectively supply a thermally conductive gas into the chamber 16 to allow controllable heat transfer across the switch 10 in use. This extends from the gas source to either the sleeve 6 or the flanges 4, 5 and to one or more tubes terminating in the chamber 16 to allow the flow of thermally conductive gas to / from the chamber 16. This can be achieved by providing a body. Alternatively, these tubes can extend through any of the conductors 2, 3 and terminate at the distal ends 13, 14 of each conductor. In the embodiment shown in FIG. 2, the gas delivery tube 15 extends through the second flange 5 and terminates inside the chamber 16. The gas source can optionally take the form of a getter or adsorption pump to help evacuate the gas as needed to open the switch. Optionally, a getter or adsorption pump can be integrated into the switch.

  The thermal expansion coefficient of each of the sleeve 6 and the flanges 4 and 5 is smaller than that of the conductors 2 and 3, and when the conductors 2 and 3 are cooled to a second temperature lower than the first temperature, the conductor 2 along the main axis 3 is reduced to form a gap 8 (not shown to scale in FIG. 3) between the proximal ends of the conductors 2,3. This separation distance occurs as a result of the difference between the thermal expansion characteristics of the sleeve 6 and the conductors 2, 3 and the physical arrangement of the components of the switch 10. In detail, the first and second conductors 2, 3 are connected to the sleeve 6 only at their distal ends 11, 12 by flanges 4, 5. Accordingly, the conductors 2 and 3 freely contract along the main axis without exerting a force on the sleeve 6 separating them. In addition, the sleeve 6 (to a lesser extent, the flanges 4 and 5) may contract when the temperature of the switch 10 is cooled to the second temperature, but this change is due to the length of the conductors 2 and 3. It should not be as much as the decrease.

  The second temperature can be considered the maximum temperature that one or each of the two conductors that guarantees the “open” state of the switch can be achieved. In fact, this can be considered the operating temperature, and is typically well below the first temperature, for example, any temperature below 100K can be included. Of course, the distal ends 11, 12 can be at different temperatures (each below the second temperature), and in practice this will typically be the case when the thermal switch 10 is in operation. . At a temperature of 10K, the stainless steel shell 6 will shrink by about 0.29%, while the copper conductors 2, 3 will shrink by about 0.31%. In a preferred embodiment, this relative difference in shrinkage will create a gap 8 of about 20 μm between the opposing faces of conductors 2 and 3 (assuming a switch length of about 10 cm as defined above). The size of the gap 8 is determined by the difference in coefficient of thermal expansion between the conductors 2 and 3 and the sleeve 6, the length of the conductors 2 and 3 along the main axis, and the temperature at which the conductors 2 and 3 are cooled. Typically, the gap is 0.05% or less of the switch length.

  The above method of constructing the gas gap thermal switch 10 with the switch design is a notable advantage in that the distal ends of the conductors 2, 3 physically connect at step 304 when the conductors 2, 3 are at approximately room temperature. Have Conversely, if the sleeve 6 is welded directly to the distal ends 13, 14 of the conductors 2, 3, as long as they are in mutual contact, the process is conducted through the conductors 2, 3 to expand them. Heat will be input to the system. Contact between the conductors 2 and 3 will eventually occur at a higher temperature. This ultimately means that a much larger gap 8 is created when the switch 10 is cooled to the second temperature, which leads to poor heat transfer performance.

  In some embodiments, the smaller gap 8 is a slight negative that decreases to zero when the thermal switch 10 is pre-stressed or pre-tensioned and partially thermally contracts to the conductors 2, 3 in step 305. Can be obtained by pressing the conductors 2 and 3 with a large force in step 303 and attaching the sleeve 6 with a fastener in some cases.

  With reference to FIG. 4, an embodiment of an assembly in which the thermal switch 10 provides specific benefits will now be described. The mechanical refrigerator in the form of a pulse tube refrigerator is indicated generally by the reference numeral 100. This can be used to cool various types of target devices, including magnet systems, experimental sensors, or other device parts of experimental applications, or to pre-cool various stages of a dilution refrigerator, for example. Such a target device 103 is shown attached to the PTR 100 via a thermal switch 10. A connection member such as a heat conduction plate can be provided between the thermal switch 10 and the PTR 100 or the target device 103 to facilitate thermal connection. A gas source 101 is also shown schematically and is arranged to provide a controllable flow of thermally conductive gas into and out of the thermal switch 10 to cause the switch 10 to operate. It can also be inside ten structures.

  In this case, the second stage of the PTR 100 is connected to the first conductor 2 of the thermal switch at the first end of the switch 10, whereas the target device 103 is connected to the second stage of the switch 10. The end is connected to the second conductor 3. Thus, the conductor 2 is cooled to a lower temperature than the second conductor 3, and a heat flow path is established across the switch 10 when the switch is closed.

  When each of the conductors 2 and 3 is cooled to a temperature lower than 100K, a gap 8 is formed between the first conductor 2 and the second conductor 3. When the thermal switch 10 is in the closed state, the thermally conductive gas is present in the chamber 16 formed by the sleeve 6 and the conductors 2, 3. As a result, heat is transferred across the switch 10 between the target device 103 and the PTR 100. This occurs first by heat conduction along each of the conductors 2, 3 and then by heat conduction using a thermally conductive gas in the region of the gap 8. Due to the low thermal conductivity of the sleeve material, negligible heat transfer occurs along the sleeve 6. In this closed state, the thermal switch 10 has an improved thermal conductivity that is superior to prior art designs because the path length that the gas must travel to transfer heat between the conductors 2 and 3 is shorter. I will provide a.

  The thermal switch 10 can be opened to thermally insulate the PTR 100 from the target device 103 by evacuating the thermal switch 10 using a controllable gas source 101. This removes the possibility of heat transfer by gas conduction between the first conductor 2 and the second conductor 3 of the thermal switch 10.

  If the switch 10 is open, a small amount of heat transfer can still occur across the sleeve 6. The amount of heat leakage depends at least in part on the characteristics of the sleeve 6 and the temperatures of the main bodies 100 and 103 connected to both ends of the switch 10. For a 20 mm diameter stainless steel sleeve 6 with a wall thickness of 1 mm and a length of 20 cm along the main axis, approximately 0 between the first body 100 at a temperature of 4K and the second body 103 at a temperature of 1K. It can be expected that 0.5 mW will be conducted. The heat leak value increases inversely with the sleeve length.

  FIG. 6 shows another embodiment of a gas gap thermal switch 10 ′, where the main reference numerals are given to indicate features equivalent to the thermal switch 10 described above. The thermal switch 10 'is similar to the previous embodiment except for two important differences.

  First, the total length of the conductors 2 ', 3' along the main axis is much larger than the total length of the flanges and their intermediate sleeves. Accordingly, the end portions 11 ', 12' extend considerably beyond the connecting members 4 ', 5' along the main axis in a direction away from the gap 8 '. The portions of the conductors 2 ', 3' that extend from the connecting members 4 ', 5' to their respective distal ends do not affect the gap size, but increase the exposed surface area of the conductors and provide better heat with the connecting device. Can be used to achieve a connection. For a switch of a given length (as measured between the distal ends of the conductors along the main axis), the intermediate sleeve and connecting flange (as shown in FIGS. 2 and 3) A smaller final gap size can be achieved by arranging to extend over a smaller portion of the conductor (as shown in FIG. 6) rather than to extend over the entire length. This is the result of a shortened conductor that freely shrinks towards the respective connecting member when cooled.

  Second, the sleeve and the second connecting member 5 'have a unitary structure. In other words, the second connecting member 5 ′ forms both the sleeve 6 and the second flange 5 of the above embodiment. Thus, the second connecting member 5 'can be configured as a single stainless steel component. Therefore, only one junction need be formed to form the chamber in step 304. This joint is formed directly between the first and second connecting members 4 ', 5' using electron beam welding. In the illustrated embodiment, the first connecting member 4 ′ functions only as a flange or collar, but in another embodiment, each of the connecting members 4 ′, 5 ′ has a connection of two sleeves and a chamber as a whole. It can have an elongated sleeve portion as formed by fusing the members 4 ', 5' together.

  In a further embodiment, the conductor extends significantly beyond the connecting member in a direction away from the gap as in the embodiment of FIG. 6, but the sleeve is at both ends of the sleeve as in the embodiment of FIGS. A separate part connected to the flange.

  Thus, as can be appreciated, a gas gap thermal switch is provided that is simpler and more robust than prior art comb designs. The method of making this thermal switch is smaller (typically between 0.5 and 1.0 mm) than was possible in the past (typically between 0.5 and 1.0 mm) and is smaller (on the order of tens of micrometers). ) Has the further advantage that a separation distance can be achieved. Therefore, when the switch is opened, effective heat transfer at the time of closing the switch can be ensured without affecting the switch capability for thermally insulating the main bodies connected to both ends of the switch.

300 Preparing the conductor 301 Fusing the conductor to the flange element 302 Aligning the conductor 303 Pressing the conductor together 304 Forming the chamber 305 Cooling the conductor

Claims (29)

A method for forming a gas gap thermal switch comprising:
(A) providing first and second conductors and first and second connecting members each having a thermal conductivity at least 5 times less than said conductor at a temperature of 100K;
(B) fusing the first conductor with the first connecting member and the second conductor with the second connecting member;
(C) aligning the conductors such that the first and second conductors extend along a common major axis;
(D) bringing the proximal ends of the aligned conductors into contact with each other when the conductors are at a first temperature;
(E) joining the first connecting member to the second connecting member so as to form a chamber around at least the proximal end of the conductor;
Each of the connecting members forming the chamber has a length of the conductor along the main axis along the main axis when the conductor is cooled to a second temperature lower than the first temperature. Having a smaller coefficient of thermal expansion than the conductor so as to decrease with respect to the length of the chamber to form a gap between the proximal ends of the conductor;
The method, wherein the switch is configured to selectively supply a thermally conductive gas into the chamber to cause activation of the switch in use.   The method of claim 1, wherein step (e) includes fusing the first connecting member to the second connecting member.   The method of claim 2, wherein the first connecting member includes a sleeve configured to surround at least the proximal ends of the first and second conductors.   The method according to claim 2 or 3, wherein the step of fusing the first connecting member to the second connecting member is performed using electron beam welding. Step (e) includes fusing each of the first and second connection members to a sleeve provided between the connection members;
The thermal conductivity of the sleeve is at least 5 times smaller than the conductor at a temperature of 100K;
The thermal expansion coefficient of the sleeve is such that when the conductor is cooled to the second temperature, the length of the conductor along the main axis decreases to form the gap. The method of claim 1, wherein   The method of claim 5, wherein the first and second connecting members are arranged as first and second flanges, respectively.   The method according to claim 5 or 6, wherein the step of fusing each of the first and second connecting members to the sleeve is performed using electron beam welding.   The method according to any of claims 5 to 7, wherein the sleeve has a thermal conductivity at least 10 times less than the conductor at a temperature of 100K.   9. A method according to any of claims 5 to 8, wherein the sleeve has a thermal conductivity at least 1000 times less than the conductor at a temperature of 10K.   The method according to claim 5, wherein the sleeve is stainless steel.   The method according to claim 5, wherein the connecting member and the sleeve are made of the same material.   (F) the length of the conductor along the main axis is reduced to form the gap between the proximal ends of the conductor to a respective temperature lower than the second temperature; The method according to claim 1, further comprising the step of cooling each one. Step (a) further comprises machining the first and second conductors to form a flat engagement surface on each of the conductors;
The method according to any of claims 1 to 12, wherein step (d) comprises bringing the engagement surfaces into contact with each other.   The method of claim 13, wherein the engagement surface extends in a plane having a normal extending along the major axis.   15. A method as claimed in any preceding claim, wherein the first and second conductors are elongated.   The gap is defined between the conductor along the main axis between the junction of the first conductor to the first connection member and the junction of the second conductor to the second connection member. 16. A method according to any one of the preceding claims, wherein the method is less than 0.05% of the total dimensions.   17. A method according to any of claims 1 to 16, wherein step (b) is performed by a brazing process.   18. A method according to any of claims 1 to 17, wherein the first and second connecting members have a thermal conductivity that is at least 10 times less than the conductor at a temperature of 100K.   19. A method as claimed in any preceding claim, wherein the first and second control members have a thermal conductivity that is at least 1000 times less than the conductor at a temperature of 10K.   The method according to claim 1, wherein the conductor is made of copper.   21. A method according to any preceding claim, wherein the connecting member is made of stainless steel.   22. A method according to any preceding claim, wherein the switch is configured to evacuate the chamber to substantially thermally shut off the opposite distal end of the conductor in use.   The method according to any of claims 1 to 22, wherein the first temperature is 280-310K.   24. A method according to any preceding claim, wherein the second temperature is 5-20K. First and second conductors aligned along a common major axis, each having a length of at least 5 cm along said major axis;
A first connecting member and a second connecting member, each having a thermal conductivity at 100K that is at least five times less than the conductor, and forming a chamber around at least the proximal end of the conductor;
A gas gap type thermal switch comprising:
Each of the connection members has a smaller thermal expansion coefficient than the conductor,
The proximal end of the first conductor is separated from the proximal end of the second conductor by a gap of less than 50 μm;
The gas gap thermal switch, wherein the switch is configured to selectively supply a thermally conductive gas into the chamber to cause activation of the switch in use. A sleeve provided between the connecting members and arranged to extend at least above the proximal end of the conductor;
Each of the first and second connecting members is fused to the sleeve;
The sleeve has a thermal conductivity at least 5 times less than the conductor at a temperature of 100K;
The sleeve has a smaller coefficient of thermal expansion than the conductor;
26. The gas gap thermal switch of claim 25, wherein the sleeve and the connecting member form the chamber. A cryogenic system,
A gas gap thermal switch according to claim 25 or 26;
A mechanical refrigerator connected to the first conductor; a target device connected to the second conductor;
A cryogenic system characterized by comprising:   A method substantially as herein described with reference to the accompanying drawings.   Apparatus substantially as herein described with reference to the accompanying drawings.

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